Shoppers afflicted by the “courgette crisis” are facing further privation, as supermarket chains Morrisons and Tesco imposed restrictions on the number of lettuces that can be bought by each customer.

Tesco has introduced a three-lettuce limit on icebergs while rival Morrisons has imposed a two-lettuce limit and banned shoppers from buying more than three heads of broccoli.

The UK’s largest retailer posted signs on its salad sections which stated: “Due to continued weather problems in Spain, there is a shortage on iceberg lettuce. To protect the availability for all our customers, we are limiting bulk purchases to three per person. We apologise for any inconvenience.”

Tesco said the signage had been sent to all its stores but was likely to be most necessary in larger outlets in city centres and towns, where sandwich shops and restaurants were likely to try to buy large numbers of lettuces due to shortages in wholesale supplies.

However, iceberg lettuces are listed as “currently not available” on Tesco’s online shopping site, and those that are on sale have generally been imported from the US, incurring hefty air freight costs.

“This is not something we want to do but we felt we had no choice,” a Tesco spokeswoman said. “We wanted to make sure that we have enough lettuces for our shoppers. In some supermarkets they are completely sold out or have nearly doubled in price.”

Morrisons said its rationing applied in all 492 stores across the UK and was intended “to restrict multiple sales to larger buyers such as restaurants, caterers and snack bars so that consumers are not losing out”.

Where they are still available in store, Tesco is selling icebergs for 79p. The standard price before the shortages was about 50p.

Sainsbury’s has just started selling US-grown icebergs for £1.40 each under the Farm Folk brand – packed by Ely-based Adventures in Food.

Aldi was selling US icebergs in some stores for 78p, but the price has nearly doubled to £1.19. Asda is also selling icebergs from the US for £1.20 each.

Photos of Tesco’s signage were posted on Twitter and Instagram. Retail expert Steve Dresser tweeted: ‘Lettuce becoming a commodity! Usually 50p each. Aldi have supply but at £1.19 each ...”

The biggest share of fresh vegetables eaten in the UK in winter comes from Murcia and Valencia in southern Spain, but the region’s crops have been hit hard by unseasonal weather, leading to courgette prices rising four-fold in two weeks. Cucumbers, artichokes, green beans and broccoli have also been affected.

Heavy rain in mid-December ruined half the lettuce harvest in Murcia. Last month the rain was followed by frost and snow – the first snowfall many residents can remember since the early 1980s – which caused some vegetable lorries to become stranded. Some Spanish growers are reported to have flown in supplies from the US in order to fulfil contracts with grocers.

Vegetable wholesalers have warned it is likely to be several weeks before supplies return to normal levels as crops grown on higher ground and hillsides become ready to pick.